The conventional computer monitor has a coil for controlling the horizontal deflection thereof. The coil does not function well in high frequency thus causing a distortion problem on the screen of the monitor. Conventionally, the distortion problem as mentioned is solved by introducing a combination of coil and capacitor. However, different combinations of coil and capacitor are required for different frequencies to correct the distortion such as in a multifrequency computer monitor. FIG. 6 illustrates a conventional horizontal deflection circuit 30 and the compensation circuit 3 therefor. The horizontal deflection circuit 30 comprises a transistor 31, a damped diode 32, an oscillating capacitor 33, and a deflection coil 34 connected in parallel. A driving signal from a horizontal driving circuit (not shown) is inputted to the horizontal deflection circuit 30. The compensation circuit 3 comprises a first coil 35 electrically connected to the deflection coil 34 of the deflection circuit 30 in series, a second coil 36 connected to the first coil 35 in series, and a capacitor 41 connected to the second coil 36 in series. A plurality of shunted capacitors 42, 43, 44, and 45 are connected to the capacitor 41 in parallel. A first switch 51 is connected to two distal ends of the second coil 36 in parallel. A plurality of switches 52, 53, 54, and 55 are respectively connected to the capacitors 42, 43, 44, and 45 and then connected to ground. The capacitors 41 to 45 have different capacitances from each other. For convenience, the switches 52, 53, 54, and 55 are respectively called the second, the third, the fourth, and the fifth switch. The switches 51 to 55 are controlled by a control circuit not shown in the figure. Suppose the frequency range is from 32 kilo-hertz to 78 kilo-hertz. The control circuit will control the ON/OFF of the switches, thus causing different combinations of the capacitors and the coils.
The capacitors and the coils combinations are illustrated with respect to different frequencies as following: